I use it in a follow-up commit to delta-encode asm.js source positions.

This commit also removes the redundant consume_bytes function.

R=ahaas@chromium.org, titzer@chromium.org
BUG=v8:4203

Review-Url: https://codereview.chromium.org/2406163002
Cr-Commit-Position: refs/heads/master@{#40157}